The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
One of the many operational schemes for passenger cars and light trucks that is under extensive study and development in response to ever increasing consumer demands and federal mileage requirements is referred to as engine start stop (ESS). This operational scheme generally involves shutting of the gasoline, Diesel or flex fuel engine whenever the vehicle is stopped in traffic, that is, whenever the vehicle is in gear but stationary for longer than a short, predetermined time, such as occurs at a traffic light.
While this operational scheme has a direct and positive impact on fuel consumption, especially for vehicles driven in cities and suburbs, it is not without complications from an engineering standpoint. For example, since the engine output/transmission input shaft does not rotate during the stop phase, automatic transmissions relying for their operation upon pressurized hydraulic fluid may temporarily lose pressure and thus gear and clutch selection and control. This shortcoming can, however, be overcome by incorporating hydraulic accumulators in the hydraulic control circuit at strategic locations. Alternatively, electrically driven gear and vane pumps may be incorporated into the transmission's hydraulic circuit to provide the required minimum pressure and flow while the engine is off. Both of these approaches have been utilized successfully.
It is apparent, however, that both of the above-recited solutions comprehend the incorporation of additional components which add both to the weight and cost of the transmission and vehicle drive train. Accordingly, it is also apparent that improvements directed to the problem of maintaining hydraulic flow and pressure in an automatic transmission during periods of engine inactivity in ESS applications are both desirable and worthwhile. The present invention is so directed.